The invention relates to a method and a circuit arrangement which enable a mechanical load applied to the motor shaft of a stepper motor or a load angle of said stepper motor to be detected in a sensor-free manner. The invention further relates to a method and circuit arrangement which enable the motor current of a stepper motor to be controlled in accordance with the load value or load angle such that the current consumption of the motor is as low as possible.
Stepper motors usually are controlled and energized independent of a current, actual motor load, i.e. a required torque, so that they generate sufficient torque for the highest motor load which is expected when a certain application occurs. Consequently, only two types of load scenarios are distinguished for such applications, i.e. motor standstill and motor operation.
Since the torque and the holding torque of a stepper motor for the most part are proportional to the RMS (root mean square) value of the motor current, multiplied by the sine of the load angle, the motor, in most situations, is operated with motor current that is much too high in relation to the current actual motor load, i.e. is operated at a torque reserve that is much too high. If, for example, the motor is operated with a mean torque reserve of 100%, i.e. with a motor current that is twice as high as required, the result, given that the power loss of the motor is proportional to the square of the motor current, is a static power loss that is increased by a factor of four. Since the mechanical power taken in stepper motors often is small compared to the static power loss, energy losses ranging from 100 to 300% are to be expected, which actually is unnecessary. While a reduction of these losses would be possible by using rotary sensors (position sensors, rotary pulse generators) and analyzing the rotational positions of the rotor, this concept is rejected for the plurality of cost-intensive stepper motor applications in which the stepper motor is used as a purely forward propelled drive and in which angle of rotation sensors thus are not required.
It is desirable to look for a possibility to lower the current consumption of a stepper motor by supplying it, based on a current actually applied motor load, with just enough current that is needed to provide the required torque.
It is desirable to provide a method and a circuit arrangement which enable a mechanical load that is actually applied to the motor shaft of a stepper motor or a load angle of said motor to be detected in a sensor-free manner.
It is desirable to provide a method and a circuit arrangement which enable the operation of a stepper motor based on a current, actual mechanical load applied to the stepper motor or a load angle of said motor such that the current consumption of the motor is as low as possible.
According to aspects of the invention, a method and a circuit arrangement are provided.
A special advantage of solutions according to aspects of the present invention is that they can be realized in a relative easy manner as a component of a known stepper motor control circuit without requiring any changes to the mechanical design of the motor or without requiring any additional mechanical components such as rotary sensors, for example.
The sub-claims contain advantageous further developments of the invention.